Bug 1355147 - Fix test moving to negative coordinates in headless mac. r=whimboo

Expose if the browser is headless to marionette session capabilities
so the tests can check headless behavior.

MozReview-Commit-ID: 10va2Iv2ytO

testing/marionette/harness/marionette_harness/tests/unit/test_window_rect.py

@@ -82,10 +82,16 @@ class TestPosition(MarionetteTestCase):
 
         os = self.marionette.session_capabilities["platformName"]
 
+        # Regardless of platform, headless always supports being positioned
+        # off-screen.
+        if self.marionette.session_capabilities["moz:headless"]:
+            self.assertEqual(-8, position["x"])
+            self.assertEqual(-8, position["y"])
+
         # Certain WMs prohibit windows from being moved off-screen,
         # but we don't have this information.  It should be safe to
         # assume a window can be moved to (0,0) or less.
-        if os == "linux":
+        elif os == "linux":
             # certain WMs prohibit windows from being moved off-screen
             self.assertLessEqual(position["x"], 0)
             self.assertLessEqual(position["y"], 0)

testing/marionette/session.js

@@ -4,7 +4,7 @@
 
 "use strict";
 
-const {interfaces: Ci, utils: Cu} = Components;
+const {classes: Cc, interfaces: Ci, utils: Cu} = Components;
 
 Cu.import("resource://gre/modules/Log.jsm");
 Cu.import("resource://gre/modules/Preferences.jsm");
@@ -267,6 +267,7 @@ session.Capabilities = class extends Map {
       ["moz:processID", Services.appinfo.processID],
       ["moz:profile", maybeProfile()],
       ["moz:accessibilityChecks", false],
+      ["moz:headless", Cc["@mozilla.org/gfx/info;1"].getService(Ci.nsIGfxInfo).isHeadless],
     ]);
   }